Person Sensor in CircuitPython

How to access the Useful Sensor's Person Sensor from CircuitPython

Introduction

The Person Sensor is a small hardware module that's intended to make it easy to find out when people are near a device, where they are, and who they are. It has an image sensor and a microcontroller with pretrained ML models that use computer vision to spot faces.

There's a detailed developer guide available, but this project has sample code that shows you specifically how to get the sensor up and running using CircuitPython. It has been tested with Raspberry Pi Pico and Wio Terminal boards, but should hopefully work on other CircuitPython-compatible platforms. If it isn't working on a board that isn't listed, it's likely to be a problem with either the pin numbers assigned to the I2C interface, or some other I2C initialization issue.

Setting up Circuit Python

You should read the official guide to setting up CircuitPython on a Pico for the latest information, but here is a summary:

• Download CircuitPython for the for your board from circuitpython.org. For example the Pico version is available at https://circuitpython.org/board/raspberry_pi_pico/. This project has been tested using the 8.0.0-beta.2 version.
• Hold down the bootsel button on the Pico and plug it into a USB port.
• Drag the CircuitPython uf2 file onto the RPI-RP2 drive that appears.

Once you've followed those steps, you should see a new CIRCUITPY drive appear. You can now drag code.py files onto that drive and the Pico should run them.

Wiring Information

Wiring up the device requires 4 jumpers, to connect VDD, GND, SDA and SCL. The example here uses I2C port 0, which is assigned to GPIO4 (SDA, pin 6) and GPIO5 (SCL, pin 7) in software. Power is supplied from 3V3(OUT) (pin 36), with ground attached to GND (pin 38).

If you're using a device that comes with a standard connector like a Qwiic or Grove interface, you should be able to use the right cable to connect to the Qwiic connector on the sensor. You can do this on the Wio Terminal with a Qwiic to Grove cable plugged into the left port (below the speaker).

Pico Wiring

For the Pico you'll need to connect directly to pins, following the wiring scheme shown below:

If you're using Qwiic connectors, the colors will be black for GND, red for 3.3V, blue for SDA, and yellow for SDC.

Running Face Detection

Copy the code.py file in this folder over to the CIRCUITPY drive. If you connect over minicom or a similar program to view the logs, you should see information about the faces seen by the sensor printed out, and messages about any errors encountered. If no faces are found, there should be output like this:

0 []

The first number is how many face have been detected, and the second part shows information about any faces that were found. Here's an abbreviated example of the output with a face present:

1 [{'box_height': 158, 'box_width': 201, 'id': -1, 'box_confidence': 99, 'box_left': ]

If your board has a built-in display, like the Wio Terminal, you should also see rectangles displayed on it when faces are detected.

Troubleshooting

Power

The first thing to check is that the sensor is receiving power through the VDD and GND wires. The simplest way to test this is to hold the sensor upright (so the I2C connector is at the top) and point it at your face. You should see a green LED light up. If you don't see any response from the LED then it's likely the sensor isn't receiving power, so check those wires are set up correctly.

Communication

If you see connection errors when running the face detection example, you may have an issue with your wiring. Connection errors often look like this:

Traceback (most recent call last):                                                    
  File "code.py", line 50, in <module>                                                
OSError: [Errno 19] No such device 

To help track down what's going wrong, you can uncomment the following lines in the script:

while True:
    print(i2c.scan())
    time.sleep(PERSON_SENSOR_DELAY)

This will display which I2C devices are available in the logs. You want to make sure that address number 98 is present, because that's the one used by the person sensor. Here's an example from a board that's working:

[36, 57, 79, 98, 104]  

You can see that 98 is shown. If it isn't present then it means the sensor isn't responding to I2C messages as it should be. The most likely cause is that there's a wiring problem, so if you hit this you should double-check that the SDA and SCL wires are going to the right pins.

Going Further

This script is designed to be a simple standalone example of reading data from the person sensor, but for your own applications you may want to check out the full library from @robotastic. This also shows how to configure options on the sensor, and access advanced features like face recognition.